(505g) Removal of Fluoride from Drinking Water Using Cellulose Acetate Pthalate -Alumina Based Mixed Matrix Membrane

Membrane technology provides attractive alternative to water purification problems. However the cost of membrane production and its operation still has been a challenge. Moreover, removal of heavy metals (like arsenic, cadmium, chromium and lead) by membrane requires the need of operations like reverse osmosis or nanofiltration. This process has their inherent limitations of high power requirements and also the removal is not achieved to a remarkable extent. This demands the rise of a new kind of inorganic additive doped- polymeric membranes which are being termed as mixed matrix membranes (MMM). Here, we exploit the adsorptive capability of the membrane along with the filtration properties. In our work, activated alumina-cellulose acetate phthalate (CAP) mixed matrix membranes was prepared for removal of fluoride from water. Fluoride is an essential micronutrient to our body, but it poses threats of harmful diseases (fluorosis), once its concentration level goes beyond 1.5 mg/l. It was observed that the removal capacity of the membrane increases significantly on alumina addition (average size of 109 µm) to the pristine CAP membrane and the maximum removal percentage was achieved at 35 % (weight) of alumina. Beyond this, the solution becomes too viscous to cast. The permeability of the membranes decreased by 53 %. This was due to the restriction of the continuity of the voids by alumina (as inferred from the SEM images). Moreover, it also decreases the segmental mobility of the polymer chains, thereby decreasing the free volume and hence the cut off. However, hydrophilicity of the membrane was improved due to the presence of particles at the surface (observed from the top view of SEM images). The surface roughness increases with alumina addition, as interpreted from the AFM images. An adsorption capacity of 2.3 mg/g (interpreted from langmuir isotherm at 25°C) was reported. Batch equilibrium was obtained at 27 hours and it follows a second order kinetics. Dynamic run of the selected membrane (area of 0.01 m², cut off 24 kDa) was made in continuous cross flow mode. The virgin membrane can provide sustained production of safe drinking water till a time of 11 hours, whereas after five cycles of regeneration, this time decreased only till 8 hours (pH: 7.2). The mechanism of fluoride removal chiefly occurs by a trade-off between adsorption and electric repulsion where the major role is played by the former. Removal efficiency is affected by presence of anions like sulphate, carbonate and bicarbonate whereas chloride and nitrate do not exert any influence. The mechanism of sieving was utilized in the removal of microorganisms like aerogenes and E.coli from tap water medium.